Disk drives are capable of storing large amounts of digital data in a relatively small area. Disk drives store information on one or more recording media, which conventionally take the form of circular storage disks (e.g. media) having a plurality of concentric circular recording tracks. A typical disk drive has one or more disks for storing information. This information is written to and read from the disks using read/write heads mounted on actuator arms that are moved from track to track across the surfaces of the disks by an actuator mechanism.
Generally, the disks are mounted on a spindle that is turned by a spindle motor to pass the surfaces of the disks under the read/write heads. The spindle motor generally includes a shaft and a sleeve into which the shaft is inserted. In order to facilitate relative rotation of the shaft and sleeve, one or more bearings are usually disposed between them.
Over the years, storage density has tended to increase, and the size of the storage system has tended to decrease. This trend has lead to greater precision and lower tolerance in the manufacturing and operating of magnetic storage disc drives.
The bearing assembly that supports the storage disk is of critical importance. One bearing design is a fluid dynamic bearing. In a fluid dynamic bearing, a lubricating fluid such as air or liquid provides a bearing surface between a fixed member of the housing and a rotating member of the disk hub. In addition to air, typical lubricants include gas, oil, or other fluids. The relatively rotating members may comprise bearing surfaces such as cones or spheres, or may alternately comprise hydrodynamic grooves formed on the members themselves. Fluid dynamic bearings spread the bearing surface over a large surface area, as opposed to a ball bearing assembly, which comprises a series of point interfaces. This bearing surface distribution is desirable because the increase bearing surface reduces wobble or run-out between the rotating the fixed members. Further, the use of fluid in the interface area imparts damping effects to the bearing, which helps to reduce non-repeat run-out. Thus, fluid dynamic bearings are an advantageous bearing system.
However, because of the lack of a mechanical connection between both ends of the shaft and support structures of the disc drive, stiffness of the rotating system can be an issue. Spindle motors having fluid dynamic bearing (FDB) designs with top cover attachment have associated problems with sealing the bearing fluid, coupling of bearing pressures, and purging ingested air.
FIG. 4 depicts a typical low cost FDB spindle motor 400 utilized in conventional hard disc drive systems. The FDB motor 400 includes a rotor 408 having one or more media discs 410 coupled thereto. The rotor 408 is disposed on a rotor shaft 406 that extends in a cantilevered orientation from a housing base 412. A conventional dual sided thrust plate bearing 402 and a counter plate 404 encloses the distal end of the rotor shaft 406 to facilitate rotation of the rotor 408 about the rotor shaft 406. As this configuration fixedly supports only one end of the shaft 406, the potential stiffness of the FDB motor 400 is limited. Thus, this type of motor may not be suitable for many high performance applications having high inertial loads or large rotating mass.
Thus, the problem presented is to increase motor stiffness to enhance disc drive performance by supporting both ends of the motor shaft while maintaining full bearing fluid levels in all bearing components.